Electrohydraulic control valve arrangement

ABSTRACT

The invention concerns an electrohydraulic control valve arrangement (10) for controlling the movement of a hydraulic motor. The control valve arrangement (10) comprises a main control valve (11), which can be actuated by the alternating application and relieving of pressure in two control chambers, and an electohydraulic servo-control valve (14) which operates with electronically controllable piston setpoint input and mechanical actual position data feedback in order to pilot the main control valve accordingly in a manner guided by the setpoint value. The servo-control valve (14) comprises a sleeve-shaped housing element (99) which is disposed so as to be moveable in a pressure-tight manner in a connection block (114) rigidly connected to the housing of the main control valve (11). The servo-control valve (14) further comprises a piston (66) which is likewise disposed so as to be moveable in a pressure-tight manner in the sleeve-shaped housing element and can be driven in alternate directions by means of a controllable electric motor (131) in order to perform incremental deflections with respect to the sleeve-shaped housing element (99) for inputting the position setpoint. The housing element (99) is coupled for movement in a positive and force-locking manner to the piston (16) of the main control valve (11). The servo-control valve (14) is provide with a valve spring arrangement (118, 119) which, in the non-controlled state of the setpoint input motor (131), sets the piston (66) in the setpoint input position associated with the operationally-neutral centre position of the main control valve (11).

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention concerns an electrohyraulic control valve arrangement forcontrolling the pressure medium input to and discharge from a linear orrotatorial hydraulic motor, with a main control valve constructed as athree position valve, which includes a piston which is displaceable inalternative directions between end positions in a bore of a housing,which correspond to the maximal values of unrestricted or unblockedcross-section of flow-through paths of the main control valve inalternative functional positions I and II, which steadily increaseessentially with increasing displacement of the piston out of a(functionally neutral) center position 0, and is correspondingly reducedwith a nearing of the piston to its center position, wherein the pistondisplacement is controllable via an electrohydraulic servo controlvalve, which is guided by an electrical setpoint value, by thealternating application and relieving of pressure in two controlchambers of the main control valve.

2. Description of the Related Art

An electrohydraulic control valve arrangement of this type is thegenerally known proportional valve ("The Hydraulic Trainer",Vogel-Publishers, Wurzburg, 1^(st) Edition 1978, pages 143-145), whichin a typical construction includes a main valve constructed as a 4/3-wayvalve and two pressure regulating valves each of which include viarespectively a proportional magnet, which produces an operating force inproportion to electrical strength, controllable pressure regulatingvalves as servo valve arrangements, via which pressure can be directedto and released from the control chambers of the main control valves.

As a result of its already discussed construction, the knownproportional valve is associated with at least the followingdisadvantages:

On the basis of the always present friction between the magnet anchorsand the housing elements of the pressure regulating valve theirrelationship is associated with a hysteresis, so that a defined value ofthe energizing current can not always in a predictable manner beassociated with a specific opening cross-section of the main controlvalve. This type of frictional effect brings about a strengthening ofthe follow or tracking error, or lag, between the setpoint position andactual position of the main control valve piston, as the time intervalis reduced, with which the energizing current changes the servo valve,in order to achieve a desired transient response of the respective valveadjustments or positions. Although extreme consequences of suchhysteresis-effects can in some respects effectively reduced or avoidedthereby, that the time period of the actuating current of the respectivecontrolled proportional magnet is varied, in such a manner, that itstemporal middle value corresponds to an effective current strength,which is associated with the desired anchor displacement, which againleads to a servo or pre-control pressure, which should produce a desiredpositioning of the main control valve piston. The anchor of a servovalve controlled in such a manner is thereby continuously kept inmovement, so that the value of the static friction, which is greater incomparison to the sliding friction practically does not come into effectand insofar as the displacement of the controlled anchor continuouslyunder the more favorable or effective secondary condition of slidingfriction is possible. Likewise, also with this type of pre-controllingor servo controlling it must be taken into account, that the actualposition of the main control valve piston accomplishes only relativelysluggishly the "middle value" of the energizing current of theproportional magnet predetermined setpoint value, since essentialagreement of setpoint and actual position can only be achieved after acertain period interval of the periodic energizing or activating currentchanges, since these are imprinted by superimposing on an alternatingcurrent varying between extreme values a direct current which correlatesto the setpoint value position to be steered or controlled. For theperiod duration of the "dither" current utilizable in practice, whichacts upon the periodic position change of the servo valve-anchor, of 10to 20 ms, this means, that-time-wise determined--equilibration of actualand setpoint value the position of the main control valve piston can beachieved only after approximately 1/20 to 1/5 second, which for numerousrequirements is too long. This is in particular true then, when thedither-amplitude of the activation current is comparable to the mediumvalue required for adjustment or setting of a pre-determined openingcross-section of through flow-path of the main control valve, that is,in cases in which the main control valve must be operated withrelatively small opening cross-sections of its flow through path.

SUMMARY OF THE INVENTION

The task of the invention is thus that of improving a control valvearrangement for the above described type in such a manner, that avirtually completely hysteresis free controlling of the main controlvalve and also a more sensible control relationship of the overallcontrol valve arrangement is achieved.

This task is inventively solved by the invention.

In accordance therewith there is provided as electrohydraulic servovalve arrangement an electrohydraulic servo control valve, whichoperates with electro-mechanically controllable position setpoint valueadvance and mechanical position actual value feedback. For realizationof this regulating principal the servo control valve includes a housingelement which is disposed so as to be moveable in a pressure-tightmanner in a connection block rigidly connected to the housing of themain control valve, as well as a piston element which for its part ismoveable in the housing element in a pressure tight manner, wherein oneof these two elements serves as a set value setpoint input element,which is drivable by means of a controllable electro-motor inalternative directions for carrying out of incremental deflections withrespect to the other element, which is drivable for its part serves asactual position data feedback element, which with the piston of the maincontrol valve is displaceably coupled in a force lock-fitting manner andthereby for carrying out with the deflection movement of the setpointvalue input element in corresponding directional manner is drivable inits servo control movement. Further, the servo control valve is providedwith a valve spring arrangement, which in the not driven condition ofthe setpoint input motor, as necessary in certain cases against a stillpresent rest-stop moment of this motor, sets or adjusts or as the casemay returns the setpoint value input element to the functional neutralcenter position of the main control valve associated setpoint valueinput signal position.

The control valve arrangement according to the invention provides atleast the following functional advantageous characteristics, to whichelucidation it is assumed, that for the setpoint input signal element ofthe servo control valve the piston thereof is used, and as actualposition data feedback element thereof the piston coaxially surroundingsleeve-shaped housing element is used, wherein the piston is driveablefor carrying out incremental deflections with respect to thesleeve-shaped housing element of the servo regulator valve by means of astep motor as setpoint input motor driven rack and pinion drive, whichsimultaneously functions as a reduction gear, and the sleeve-shapedhousing element of the servo regulator valve--without play--is moveablycoupled with the piston of the main control valve in such a manner, thatits deflections follow those of the setpoint input piston, wherein thesleeve-shaped housing element for its part can be moveably coupled withthe piston of the main control valve via a gear, so that with a definedconversion relationship deflections of the main control valve piston canbe converted into therewith controlled servo movements of thesleeve-shaped housing element of the servo control valve. In accordancewith this function there is accomplished both the servo control valve,independent of changing the sense of the setpoint input and that of thepiston position of the main control valve respectively then in itsfunctional neutral middle position, when correspondence of the actualposition of the main control valve piston with its setpoint value isgiven, which via step motor controlled displacement of the setpointinput piston the servo control valve was guided in. Thereby thehysteresis effect of the type described in the introductory portion ispractically avoided. The step width of the incremental deflections ofthe setpoint input piston of the servo control valve is controllableelectronically in a simple manner and with respect to its value ispredictably setable or pre-determinable in a broad range, so that asufficient fine stepped, quasi continuously adjustability of the maincontrol valve with regard to the required flow-through cross-section ispossible. Problems, which in the known proportional valve result from a"humm" (dither-current)--modulation of magnet energizing current, inprincipal do not occur in the control valve arrangement according to theinvention.

By means of the valve spring arrangement of the servo regulator valve,which returns or resets the setpoint input piston to the neutral centerposition of the main control valve associated setpoint value-controlsignal position as soon as a driving thereof by means of a setpointinput signal motor ceases, it is in a simple manner achieved that ahydraulic drive unit controlled via the inventive control valvearrangement ends up in a secure position with the turning off of thesetpoint input signal control, even when the driving or operatingpressure source remains in operation.

By means of the characteristics or features of alternative embodimentsof the control valve arrangement discussed below, in which therespective position feedback element of the servo control valve can berigidly connected with the piston of the main control valve and in thismanner a particularly simple construction of the control valvearrangement is achieved.

Alternatively, however, the main control valve of the control valvearrangement can be constructed as a rotating slide valve and the servocontrol valve can be constructed as a linear slide valve, in which casea drive unit is provided, which converts the azimuthal displacements ofthe piston of the main control valve into linear displacements of thefeedback element of the servo control valve.

For the control valve arrangement, a constructively simple and preferredembodiment, of which the main control valve is constructed as a lineardisplacement valve and the servo control valve as a rotating slidevalve, of which the actual position data feedback element via a couplingarrangement, which linear displacements of the piston of the maincontrol valve convert into azimuthal displacements of the actualposition data feedback element of the servo control valve, with whichthe main control valve piston is motion coupled, wherein the setpointinput signal element of the servo control valve is connected secureagainst rotation with the drive shaft of the electrical setpoint inputmotor, are via the characteristics of advantageous simple embodiments ofthe coupling device discussed below are given, by means of which theactual position data feedback element of the servo control valve ismotion-coupled with the piston of the main control valve. A staying,bracing or fastening assembly envisioned in combination herewith, bymeans of which the play of the movement coupling between the piston ofthe main control valve and the actual position data feedback element ofthe servo control valve is achievable, is realized in a preferredtechnically simplified and space saving embodiment according to thecharacteristics of further preferred embodiments.

For the valve spring arrangement which, when the setpoint input signalelement of the servo control valve is not in the condition of beingcontrolled the setpoint input signal motor, urges to the functionalneutral center position of the main control valve piston associatedsetpoint input signal position, are the alternatively or in combinationutilizable embodiments, which in particular are suitable, when the servocontrol valve of the control valve arrangement is constructed as alinear slide valve, while via the characteristics of other embodiments afunction corresponding or suitable valve spring arrangement is given,which is particularly suitable for the servo control valve of thecontrol valve arrangement constructed as rotating sliding valve.

BRIEF DESCRIPTIONS OF THE DRAWINGS

Further details of the control valve arrangement according to theinvention can be found in the following description of two specialembodiment examples with respect to the drawings. There are shown:

FIG. 1 a first embodiment of a control valve arrangement whichintroduces the function of a proportional valve with a main controlvalve constructed as a linear slide valve and a likewise as linear slidevalve constructed servo control valve as servo valve in schematicsimplified longitudinal sectional representation;

FIG. 1a a hydraulic diagram of connections for explanation of thefunction of the servo valve arrangement according to FIG. 1;

FIG. 2 a further illustrative embodiment of a control valve arrangementwhich is the functional analog of the control valve arrangementaccording to FIG. 1 with a main control valve constructed as a linearslide valve and a servo control valve constructed as rotating slidevalve, in a cross-sectional representation according to FIG. 1;

FIG. 2a a valve spring arrangement of the servo control valve accordingto FIG. 2 through which this, in the not driven condition of thesetpoint input motor, is found in the indicated configuration, whichcorresponds to the setpoint input of the neutral central position of themain control valve, partially in section along the Lines IIa--IIa ofFIG. 2;

FIG. 2b an operating lever spring or spring clip of the valve springarrangement according to FIG. 2a in its tensioned condition, insimplified perspective representation and

FIG. 2c a section along the Lines IIc--IIc of FIG. 2 for explanation ofa free of play movement coupling of the piston of the main control valvewith an actual position data feedback element of the servo control valveof the control valve arrangement according to FIG. 2 illustrated bracingdevice.

DETAILED DESCRIPTION OF THE INVENTION

The electrohydraulic control valve arrangement which in FIG. 1 isreferenced overall with 10 encompasses a main control valve, indicatedoverall with 11, which is operable by hydraulic pressure, which isswitchable or reversible by alternative application and relieving ofpressure in control chambers 12 and 13 from its represented startingposition 0 into alternative functional positions I and II, as well as aservo valve and overall with 14 indicated servo control valve, whichfunctions with electrical input signal the set position of the piston 16of the main control valve 11 and mechanical feedback of the actualposition of the piston 16.

For the purpose of explaining it is assumed that the control valvearrangement 10, as can be seen from the flow diagram or connectionschematic of FIG. 1a, is employed for the operating control of arotational hydro-motor 17, of which the alternative rotationdirections--clockwise and counterclockwise--are associated with thealternative functional positions I and II of the main control valve 11,wherein the rotational speed of the motor is adjustable by volume offlow of the hydraulic drive medium supplied to and withdrawn from it viathe main control valve 11.

The resting condition main control valve 11 as shown with referencenumber 0 in FIG. 1a is associated with the resting condition of therotational hydro-motor 17.

The main control valve 11 is constructed as a linear slide valve, ofwhich the piston 16 is slidingly displaceable back and forth in thedirection of the central longitudinal axis 18 in a housing bore 19 whichextends between the control chambers 12 and 13, wherein with respectthereto the end positions are defined by impacting of end pieces 21 and22 of piston 16 with the respectively oppositely lying wall surfaces 23or as the case may be 24 of the control chambers 12 and 13.

The main control valve 11 is constructed as a 4/3-way valve, in itsshown resting position 0 with the pressure exit of a not shown pressuresupply aggregate associated P-supply connection 26 and with thepressureless supply chamber of the pressure supply aggregate associatedT-return flow connection 27 as well as against an A-control connection28 as well also against a B-control connection 29 of the main controlvalve, which through its alternative application and relieving ofpressure accomplishes the drive control of the utilizer 17, is closedoff. In the design of the main control valve selected for purposes ofexplanation this achieves via a through pressure impacting of theaccording to the representation in FIG. 1 right control chamber 13 andpressure relieving of the left control chamber 12 desired displacementsof its piston 16 to the left in its functional position I in which theP-supply connection 26 of the main control valve 11 via a through flowpath 31, with an A-control connection 28 and the T-return flowconnection 27 via a further flow through path 32 with the B-controlconnection 29 of the main control valve 11 is connected; by pressureimpacting of the left control chamber 12 and pressure relieving of theright control chamber 13 of the main control valve 11 this accomplishes,beginning from the represented starting position 0 in its functionalposition II, in which via a first through flow path 33 of the P-supplyconnection 26 is connected with the B-control connection 29 and via asecond through flow path 34 of the T-return flow connection 24 of themain control valve 11 with the A-control connection 28 thereof isconnected.

The main control valve 11 is constructed as a proportional valve, inwhich with increasing displacement of its piston 16 away from the restposition 0 corresponding central position, each according to directionof the displacement thereof, which in the alternative functionalposition I and II released through flow paths 31 and 32 or as the casemay be 33 and 34 with increasing larger cross-sections are unrestrictedor unblocked, which in the end positions of the piston respectivelyachieve their maximal value.

For achievement of this function the main control valve 11 isconstructed in conventional manner as follows:

The housing bore 19 of the main control valve 11, in which its piston 16with piston flanges 36, 37, 38 and 39 is pressure tight slideablyguided, which flanges are pair-wise rigidly connected with each otherthrough piston rods 41, 42 and 43 of which the cross-section is smallerthan that of the housing bore 19, has a central cross-section 19', whichextends between housing side control surfaces or edges 44 and 46, whichare formed by the bore side edges each other adjacent side walls ofcontrol notches 47 and 48 of the valve housing 49, which arerespectively in constant communication with the control connections 28and 29 of the main control valve 11. Their inner bore sections 19' formthe radially outer, housing tight bordering of a ring space or cylinderdisplacement space 51 which stays in constant communication connectionwith the P-supply connection of the main control valve 11. This cylinderspace 51 is axially moveable via the borders of each other adjacent ringend surfaces of the through the middle piston rod 42 with each otherconnected central piston flanges 37 and 38, which with the outer edgesof their each other adjacent or neighboring ring end surfaces on thepiston side, form inner control edges 52 and 53, of which axialseparation corresponds respectively to those of the inner control edges44 and 46 of the A-control notch 47 and the B-control notch 48.

The A-control notch 47 and B-control notch 48 of the valve housing 49enclose via respectively a through the radial inner edge of its axialouter notch flank delineated, outer control edge 54 or as the case maybe 56 at bore section 19" or as the case may be 19'", which form housingtight radial borders or edges of cylinder space 57 and 58, which via ahousing channel 59 are coupled in communication with each other andlikewise coupled to the return flow connection 27 of the main controlvalve 11.

In the direction of the central longitudinal axis 18 of the housing bore19 measured thinness breadth of the A-control notch 47 and the B-controlnotch 48 of the main control valve housing 49 corresponding the axialthickness of the two central piston flanges 37 and 38 of the maincontrol valve piston 16, of which the ring face surfaces facing awayfrom each other with their radial outer edges axially form outer controlsurfaces 61 and 62, which in the represented rest position 0 of the maincontrol valve 11 likewise are the axial inner control edges 52 and 53 ofthe inner piston flange 37 and 38 in null overlap with the housing sidecontrol edge 54 and 56 or as the case may be 44 and 46, so that in thisrest position 0 both of the pressure supply aggregate constantlycommunication connected ring spaces 57 and 58 are closed off from thepressureless supply chamber against the housing side control notch 47and these from their side against the central, with the P-supplyconnection 26 communicating connected ring space 51 of the main controlvalve.

The pressureless supply chambers of the supply aggregate connected withT-ring space 57 and 58 are pressure tight moveably sealed off by the endflange 36 and 39 of the piston 16 of the main control valve 11 againstthe control chamber 12 and 13 thereof.

If in the, according to the representation in FIG. 1, right controlchamber 13 pressure is supplied and in the left control chamber 12pressure is released, whereby the piston 16 of the main control valve 11experiences a displacement towards the left, then the main control valvecomes to be in one of the functional position I correspondingarrangements of the piston side and the housing side control edges, thatis, the A-control notch 47 in communicating connection with the ringspace 51 under high pressure and the B-control notch 48 in communicatingconnection with the right T-ring space 56.

By the pressure impacting of the left control chamber 12 and relievingof the right control chamber 13 the main control valve 11 is moved toits functional position II, in which the A-control notch 47 is incommunicating connection with the left T-ring space 57 and the B-controlnotch 48 with the central T-ring space 51.

The amount or value of the in the alternative through flow position Iand II derestricted cross-section of the flow through path 31 and 32 oras the case may be 33 and 34 of the main control valve 11 is adjustableby means of the servo control valve 14, by means of which the pressureimpacting and releasing of the control chambers 12 and 13 of the maincontrol valve 11 are controllable. The servo control valve 14 isconstructed in the here represented, special embodiment in substantialconstruction analogy to the main control valve 11 as linear slide valve,which is provided with parallel a progress or flow of the centrallongitudinal axis 68 the central longitudinal axis 18 of the maincontrol valve 11. Also, the servo control valve 14 repeats the functionof or serves as a 4/3-way valve, for which in overall with 66represented piston and its housing 99, apart from the cross-sectionalmeasurement of a larger axial spacing apart of the central pistonflanges 87 and 88, extends between with the T-ring space 101 of theservo control valve 14, providing with the same configuration of pistonside control edge or surface 102, 103, 111 and 112 as well as housingside control edge 94, 96, 104 and 106, as in the main control valve 11.The same holds in the sense for all this type of element of the servocontrol valve 14, which in FIG. 1 as well as la is filled in withreference numbers, which in comparison to the respective referencenumbers, with which the already described construction and functionalelements of the main control valve 11 are occupied, are increased by 50,so that with respect to the description of the with the increasedreference number provided elements of the servo control valve 14reference can be made upon the description of the main control valve 11,in order to avoid unnecessary repetition.

The housing 99 of the servo control valve 14 is formed with an outercylindrical housing, with a central longitudinal axis 68 of the servocontrol valve 14 co-axial bore 113 of a housing block 114, which isconnected rigidly with the housing 49 of the main control valve 11,pressure-tight sliding back and forth is displaceably guided.

The A-control connection 78 is connected with the control chamber 13 ofthe main control valve according to FIG. 1, while the B-controlconnection 79 of the servo control valve 14 is connected with the leftcontrol chamber 12 of the main control valve 11. The appropriateconnecting channels are referenced with numbers 116 or as the case maybe 117.

The piston 66 of the servo control valve 14 has a middle positioncentered by valve springs 118 and 119, which is the setpoint inputsignal position for the there represented starting position of thepiston 16 of the main control valve 11, which via a schematic indicatedbridge 121 is connected against movement with the housing 99 of theservo control valve 14.

This assignment of the rest or starting position 0 of the servo controlvalve 14 and the main control valve 11 is achieved by the precision ofthe construction as well as in certain cases the adjustability of themechanical connection between the main control valve piston 16 and thepiston 66 of the servo control valve 14 as well as the adjustability ofthe rest position of the valve piston 66 of the servo control valve 14.With respect thereto adjustability of the piston position is indicatedin FIG. 1 by a position set screw 122, by means of which the supportblock 123, on which the one valve spring 118 on the housing side issupported, is axially displaceable, while the other valve spring 119axially supports on the oppositely lying wall face 124 the housing block114 containing servo control valve 14.

The piston 66 is on its one, according to FIG. 1 right end with aslender, rod-shaped, right valve spring 119 centrally through-goingextension 126 provided, which extends through a central bore 127 of theend surface wall 124 and at its free end is constructed as a rack 128,of which the teeth are in engagement with the drive pinion 129 of anelectric step motor 131 in a free of play combing engagement.

The step motor 131 is by output impulses of an electronic control unit132 controllable for carrying out incremental rotational movements inthe possible alternative rotational directions.

By a controlling or driving of the step motor 131 in the arrow 133represented rotational direction (+) φ₁ the valve piston 166 of theservo supply valve 114 experiences, with respect to the representedstarting position 0 a deflection ε₁, correlated with this angular amountφ₁, in accordance with the representation of FIG. 1 to the left, wherebythe functional position I of the servo control valve correspondingconfiguration its valve piston 66 and its sleeve-shaped housing element99 is achieved, with the consequence, that via the A-control connection78 the servo control valve 14 changes pressure in the right controlchamber 13 of the main control valve 11 and the left control chamber 12thereof via the B-control connection 79 of the servo control valve 14 isrelieved of pressure. The main control valve piston 16 and the with thisfixed against displacement connected, sleeve-shaped valve housingelement 99 of the servo control valve 14 experienced thereby likewise adeflection "to the left" following the deflection ε₁ of the piston 66 ofthe servo control valve 14, which comes to rest, as soon as the piston66 and the sleeve-shaped housing element 99 of the servo control valve14 again in the represented end position 0 corresponding configurationcoincide, that is, the main control valve piston 16 has carried out thesame deflection ε₁ to achieving the function position I of the maincontrol valve 11 as the piston 66 of the servo control valve, which viathe electric input control signal has correspondingly displaced thesetpoint value.

In an analogous manner the main control valve 11 is in its functionalposition II controllable and on defined value the opening cross-sectionof the in this functional position II made free flow through path 33 and34 is adjustable.

The A-control coupling 78 and the B-control connection 79 of the servocontrol valve 14 as well as its P-supply connection 76 and its T-flowback connection 77 mouth or connect within flat or shallow ring notches134 and 136 or as the case may be 137 and 138 of the housing block 114,which are in communicating connection with the A-connection channel 116and the B-connection channel 117 or as the case may be the P-supplyconnection 76" and the T-return flow connection 77' of the immovablehousing block 114 and in axial direction "on both sides" of the instarting position 0 of the main control valve 11 associated middleposition of the sleeve-shaped housing element 99 of the servo controlvalve are so far displaced, that their respective coupling connectionswith the valve spaces 101, 107 and 108 in various possible displacementpositions of the housing 99 is achieved. In a typical arrangement of thecontrol valve arrangement 10 the maximal deflections ε_(1max) andε_(2max) of the piston 66 of the servo control valve 14 out of itsspring centered middle position, with which also appropriate maximaldeflections of the main control valve piston 16 and the with thisfixedly connected servo control valve housing 99 is coupled,respectively 90° rotations of the drive pinion 129 of the step motor 131in clockwise direction and in counterclockwise direction, wherein this90° rotation, controlled by the electric control unit 132 is dividedinto respectively 100 incremental steps of equal amount. The herewithcoupled stepability of the opening cross-section of the main controlvalve 11 in its both functional positions I and II correspondspractically a continuous variability of the opening cross-section of therespective flow through path.

The valve springs 118 and 119 which engage the as setpoint value servoelement employed valve piston 66 of the servo control valve 14 are sopositioned or adjusted, that they in the not energized condition of thestep motor 131 are in condition, to overpower the rest detainingmovement thereof and to bring the valve piston 66 in the neutral middleposition thereof, with a consequence, that, as long as pressure supplyis in condition, also to bring the main control valve back to itsresting position 0. In order to achieve this position of the maincontrol valve piston 16 also in lost pressure supply, it is effective oruseful, when also the rest position 0 of the main control valve piston16 and with this respectively the valve housing 99 of the servo controlvalve 14 via valve springs 141 and 142 of the main control valve 111,which can be significantly weaker constructed than the valve springs 118and 119 of the servo control valve 114, to center by the springs.

The in FIG. 2, in which individual details can now be omitted, asfurther embodiment represented, in general with 10' indicated controlvalve arrangement is functionally in large part analogous to controlvalve arrangement 10 according to FIG. 1 and differs from it essentiallyonly in the construction or design of the servo control valve 14' asrotating sliding valve and the hereby necessary construction of thepiston 16' of the main control valve 11' which communications ortransmits the movement coupling of the same with the position--actualvalue--feedback element 99' of the servo control valve 14'.

Insofar as for elements of FIG. 2 the same reference numbers are givenas the already in FIG. 1 described elements, reference should be made tothe description given with respect to FIG. 1. By the utilization ofreference numbers, which are provided with a (') , with respect to theirnumber however are identical with reference numbers found in FIG. 1described construction and functional elements of the control valvearrangement 10, reference should be made to their construction and/orfunctional analogy.

In the servo control valve 14' of the control valve arrangement 10'according to FIG. 2 there is achieved the setting or controlling of thesetpoint value of the position of the piston 16' of the main controlvalve 11' by rotating its central piston 66' about the centrallongitudinal axis 68' of the servo control valve 14, which with a to thecentral longitudinal axis 18 of the main control valve 11' rightangularly flow of its central longitudinal axis 68' to the main controlvalve 11' is connected or associated. The return signal of the actualvalue of the position of the piston 16' of the main control valve 11' isachieved or accomplished by the "rotating with" of the basically orbasic construction according to cylindrical sleeve-shaped housingelement 99' of the servo control valve 14' about the centrallongitudinal axis 68' thereof, wherein the conversion of translationalmovement of the main control valve piston 16' along the centrallongitudinal axis 18 thereof in rotatoric movement thereof as returnsignal element used housing part 99' of the servo control valve 14' byform fitting engagement of a with this sleeve or casing shaped rotatablehousing part 99 of the servo control valve 14' fixedly connectedcoupling element 143 with a ring notch 144 of the main control valvepiston 16' comes to assemble or to the condition, that in the middlearea or realm the relative longitudinal extending of the piston flange36' is associated, which forms for the one part the pressure tightmoveable boundary of the left control chamber 12 and for the other partalso the one-left-pressure tight moveable boundary of the left T-ringspace 57 of the main control valve 11'.

The piston 66' of the servo control valve 114 serving as setpoint valueservo element is fixedly connected with the drive shaft 146 of the stepmotor 131 which via an outer straight gear teething with an innerstraight gear teething of the piston 66' with this is in free of playcombing engagement.

The setpoint value servo piston 66' of the servo control valve 14',which is pressure tight rotatably guided in the central through-goingbore 69' of the sleeve-shaped housing element 99', which for its part ispressure tight rotatably guided in the connection lock 114' of the servocontrol valve 14' central through-going bore 113' of the connectionblock 114 of the servo control valve 14' about its central longitudinalaxis 68', is rotatably connected with an overall with 147 indicated backsquare, which between free shank ends 148 and 149 (FIG. 2a and FIG. 2b)an overall with 151 indicated shank spring extends into, which is underan azimuthal pre-tensioning, via which the free shank ends against eachother directed azimuthal forces are directed and against each otherfacing away from each other contact surfaces or impinging surfaces ofthe back square 147 are urged. The shank spring 151 is detained againsta rotating about the central longitudinal axis 168' and communicatesthereby, both by its pre-tensioning, which is sufficient, in order in aelectrically de-energized condition of the step motor 131 from thisstill present arresting moment to overpower the effect, that thesetpoint input piston 66' in the de-energized condition of the stepmotor 131 returns to the in the FIG. 2 and 2a represented, definedazimuthal position φ₀, which in the represented, neutral middle position0 of the main control valve 11' is associated as setpoint input signalposition.

The return arrangement 147 formed of the shank spring 151 and the backsquare 147, functionally the valve spring 118 and 119 of the "linear"servo control valve 114 according to FIG. 1, corresponding returnassembly 147, 151 of the rotating sliding-servo control valve 14'according to FIG. 2 is in greater detail realized as follows:

The back square 147 includes or encompasses a stable, a section of thedriven shaft 146 of the step motor 131 coaxially encompassing fixingcasing 152, which on its valve side end is provided with an innerstraight teething or gearing, which is in combing or inner digitatingengagement with a short section of the outer straight teeth or gears ofthe drive shaft 146 of the step motor 131 and thereby is connected fixedagainst rotation with this drive shaft 146. The fixing casing 152 issecured against rotation against axial slippage with respect to thedrive shaft 146 via grub or headless screws 153. From the motor side,flange shaped edge 153' of the fixing casing 152 of the back square 147there extends a radial flat rod shaped shank 154, on the radial outerend of which and with a to the radial shank 154 right angled towards thevalve end directed path of a round rod shaped back bore impact shank 156engages the impact angle or back square, wherein the central axis 157 ofthis impact shank 156 runs parallel to the central longitudinal axis 68'of the servo control valve 114.

The shank spring 151 has with the central axis 68' of the servo controlvalve 14 coaxial windings 158 of like internal cross-section, which inthe represented, special embodiment is the same as the cross-section ofthe bore 113' of the attachment or coupling block 114' of the servocontrol valve 14'.

Radially outside of the from the windings 158 of the shank spring 151enclosed cylindrical area there are in respect to the centrallongitudinal axis 68' of the servo control valve diametric arrangementan anchor plug or projection 159 and an impact plug 161 with circularround cross-section provided, which both from one of the 131 motor or asthe case may be impact angle or back square 147 facing side theattachment block 114' of the servo control valve 14' are spaced. Thecentral longitudinal axis 162 of the anchor plug and the centrallongitudinal axis 163 of the abutment plug 161 run parallel to thecentral longitudinal axis 68' of the servo control valve 14', whereinvia the central longitudinal axis 163 of the abutment plug 161 and thecentral longitudinal axis 68' of the servo control valve 14 a "central"radial plane 164 is defined, in which also the central longitudinal axis157 of the abutment shank 156 of the abutment angle or back square 147extends, as well as also the radial middle plane 166 thereof, when thecentral piston 166' of the servo control valve 14 is situated in itscentral or base position 0 of the main control valve 11 arrangedsetpoint input position.

The shank spring 151 has, as can also been seen from the detailedrepresentation in FIG. 2b, in the illustrative embodiment representedfor explanation, four "inner" closed to themselves windings 158, whichrun in radial separation from the fixing casing 152 of the back square147 and this respectively with the full circumference angle of 360°enclose, as well as on each end face side of the shank spring anend-winding 167 or as the case may be 168, which, with respect to thehousing or casing attached, via the central longitudinal axis 68' and163 of the servo control valve 14' or as the case may be the abutmentplug 161 marked radial plane 164 of the orientation φ₀ only over a partof the circumference of the inner windings 158 extending. On these endside partial windings 167 and 168 are attached or locked on, as can bestbe seen in FIG. 2a, with flat bending, which corresponds approximatelyto that of the abutment tap 161, which radially or approximatelyradially extending free shank end 148 and 149 of the shank spring 151.

One of the central windings, which between two "complete", the fixingcasing fully enclosing windings 158 is positioned, is within anazimuthal angular area of in total of approximately 60° provided with aU-shaped radial bulge 169, through which the anchor plug or tap 159,which the abutment plug 161 diametrically oppositely is oriented, fromthe outside form fittingly engages about is provided the shank spring151 in the arrangement shown in FIG. 2a is ensured against a rotationabout the central longitudinal axis 68' of the servo control valve 14'.

In the FIG. 2b represented tensioned condition of the shank spring 151corresponding configuration the partial winding 167 and 168 extendedonly over a--upon the between the free shank ends 148 and 149 extendinglongitudinal plane 171 with respect to--circumference area ofapproximately 160°, so that between their free shank ends 148 and 149 a"thinner" azimuthal separation of approximately 40° remains, that is, apositive overlapping of the end position partial windings 167 and 168 incircumference direction is not given.

In order to provide necessary azimuthal pretensioning for the operatingfunction of the shank spring 151, namely in the de-energized conditionof the step motor 131 to rotate the setpoint input piston 66' of theservo control valve 14' in that orientation, which is associated withthe base position 0 of the main control valve 11', the shank spring 151is sent, that this during the assembly in the broken lines shownconfiguration in FIG. 2a is brought, in which the outer, end terminalpartial windings 167 and 168, radial within the abutment plug 161 onthese passing by on one through these cross-section dependentcircumscribing overlapping and with radial extending free shank ends 148and 149 themselves respectively on each other facing away from eachother sides of the abutment plug 161 on this--azimuthal--supporting.

After this configuration of the shank spring 151 is set and the baseposition 0 of the main control valve 11' corresponding position of itspiston 16 as well as the therewith associated piston of the returnsignal element 99' of the servo control valve 14 and also with the baseposition 0 of the servo control valve 14' associated azimuthal positionof its setpoint input piston 16' is set or dialed in, which can beaccomplished without requiring special instructions, the step motor 131with that orientation of its back square 147 is so seated, in which theabutment shank 156 of the back square 147 radial outside of the abutmentplug 161 between the free shank ends 148 and 149 of the partial windings167 and 168 engages and in this position on the housing block 114' ofthe servo control valve 14 is secured, whereby the radial orientation φ₀of the radial plane 164 of the back square 147, which with the driveshaft of the step motor 131 is fixed against rotation, the base rotation0 of the servo control valve 14 and therewith also the main controlvalve 11 is properly functionally associated.

The servo control valve 14 is so constructed, that it via a by means ofthe step motor 131 controlled rotation of its central valve piston 66'in the direction of the arrow 172 of the FIG. 2a, that is, seen in thedirection of the arrow 173 in FIG. 2, in rotational sense in itsfunctional position I standing, in which the right control chamber 13 ofthe main control valve 11' via the A-control connection 78' of the servocontrol valve 14' is placed under pressure and the left control chamber12 of the main control valve 11 via the B-control connection 79' of theservo control valve 14 is relieved of pressure, with a consequence, thatalso the main control valve 11 with an azimuthal deflection of thecentral piston 66 of the servo control valve 14 associated axialdeflection with respect to the base position of its valve piston 16' inthe functional position I is steered. In an analogous manner the maincontrol valve 11' is through step motor controlled azimuthal rotation ofthe central piston 66' of the servo control valve 14' controllable inthe direction of the arrow 174 in FIG. 2a in its functional position II,in which its valve piston 16', with respect to its neutral centralposition 0, experiences a deflection "towards right" which with theazimuthal deflection of the central servo control valve piston 66' ismonotonically correlated.

The main control valve 11' and the servo control valve 14' of thecontrol valve arrangement 10' according to FIG. 2 is configured withrespect to each other that the maximal deflections ε_(1max) and ε_(2max)of the piston 16' of the main control valve 11' in the sense of itsinput the functional position I or II azimuthal deflection φ_(1max) orφ_(2max) of the piston 66' in the direction of the arrow 172 or as thecase may be 174 of FIG. 2a correspond, which respectively have a valueof 30°, which in FIG. 2a through azimuthal orientation φ_(1max) andφ_(2max) of the radial central plane 166 of the back square 147 of theservo control valve 14' represents.

The for translatorial conversion, in the direction of the centrallongitudinal axis 18 of the main control valve 11' resulting movement ofthe piston 16' in rotatoric "feedback" movement of the sleeve-shapedfeedback housing element 99' of the servo control valve 14' providedcoupling element 143, there is formed as a slender, from the circularring shaped face edge 176 of the sleeve-shaped feedback housing element99' of the servo control valve 14' extending, on its end with a ballshaped head 177 provided staff 178, of which the central longitudinalaxis 179 runs parallel to the central longitudinal axis 68' of the servocontrol valve. The diameter of the ball shaped head 177 of the couplingelement 143 corresponds, aside from a reduction of a few hundredths ofmillimeters with the thinner breadth of the ring notch 144 of piston16', into which the coupling element 143 radially or approximatelyradially extends. The thickness of the staff shaped part 178 of thecoupling element 143 is smaller than the cross section of its ballshaped head 177. The radial separation r of the central longitudinalaxis 179 of the coupling element 143 from the central longitudinal axis68' of the servo control valve 14', which cumulatively must be satisfiedwith the relationship

    r≧ε.sub.max /sin(φ.sub.max)

when valid, that ε_(max) =ε_(1max) =ε_(2max) and likewise φ_(max)=φ_(1max) =φ_(2max), has in this for illustration selected example thevalue r=2 ε_(max).

The radial separation r_(max), in which the central longitudinal axis 68of the servo control valve 14' runs from the central longitudinal axis18 of the main control valve is given by the equation ##EQU1## In thisarrangement of the servo control valve 14' and the main control valve11' to each other, the values about which the ball shaped head 77 of thecoupling element 143 with respect to the central longitudinal axis 18 ofthe main control valve 11' represent, parallel to the centrallongitudinal axis 68' of the servo control valve 14' extendinglongitudinal central plan of the piston 16' of the main control valve11' in alternative directions--"towards up or down" can be deflected,each being equal, so that in each azimuthal position of thesleeve-shaped housing element 99' of the servo control valve 14' anapproximately central positioning of the ball shaped head of thecoupling element 143 in the ring notch 144 of the piston 16' of the maincontrol valve 11' results.

In order to achieve for a precise function of the control valvearrangement 10' suitable freedom from play of the movement couplingbetween piston 16' of the main control valve 11' and the sleeve-shapedhousing element 99' of the servo control valve 14', there is provided a,functioning as a torsion spring, shown generally with 181, tensiondevice, which exercises azimuthal supported torque, upon thesleeve-shaped housing element 99' of the servo control valve 14' a tothe central piston 66', which fixed against rotation with the driveshaft 146 of the step motor 131 is connected, on the basis of which thehead 177 of the with the sleeve-shaped housing element 99' fixed againstrotation is connected to coupling element 143 dependably is held inabutment with the single notch wall 182 of the ring notch 144 of thepiston 16' of the main control valve 11'. This tensioning device 181 forwhich discussion or illustration reference can also be made to FIG. 2cencompasses an outer helical spring 183 standing under pull pre-tension,which upon an azimuthal area, which approximately is smaller than the tothe total pivot area φ_(1max) -φ_(2max) of the sleeve-shaped housingelement 99' of the servo control valve 14 to 3600 complimentary angle,from an outer, concave ridge 184 of an axial direction only slightlyescavated, from the central bore 113' of the connection block 114' ofthe main control valve 11' projecting end section 186 (FIG. 2) of thesleeve-shaped housing element 99' is received. The bending radius ofthis ridge 184 is slightly larger than that of the spring coils, whichwith the radial inner 180° area of this concave ridge 184 are receivedand on its ground are supported. The short end section 186 of thesleeve-shaped housing element 99 of the servo control valve 14 servingas mechanical feedback element extends through an opposite to thecentral bore 113' of the housing block 114 of the servo control valve14' in which the sleeve-shaped housing element 99' in segments of itslength pressure tight sliding is rotatably provided, further bore steps187, of which the cross-section is slightly larger than the outerdiameter of the helicoil spring 183 wherein the radial thinness width ofthe between the bore steps 187 and the outer coating or jacket surfaceof the coil spring 183 carrying end section 186 of the sleeve-shapedhousing element 99' remaining ring cleft 188 is smaller than thecross-section or diameter of the individual spring coils, which have aspring wire thickness of 0.2 mm to approximately 2 mm. Thereby the coilspring 183 is against an axial pushing out of the ring cleft 188sufficiently secured. In the central valve piston 66' there is thereinfrom the end section 186 of the sleeve-shaped housing element 99' on theazimuthal area of approximately 300° co-axial encompassed, out of thecentral bore 113' of the connection block 114' to the main control valve11' extending area an abutment rod 189 securely seated, which on oneside radially extends into the "free" ring cleft area 188', thisazimuthal width through the azimuthal separation radial end face surface191 and 192 is determined, which itself in axial direction over thedepth--axial gap--of the coil spring 183 carrying end section 186 of thesleeve-shaped housing element 99' of the servo control valve 14'extending.

The design of the sleeve-shaped housing element 99' of the servo controlvalve 14', and the orientation of the rigidly with the setpoint inputpiston 66' of the servo control valve 14' connected abutment rod 189, isso determined based upon the other, that in the equilibrium ofposition--setpoint value and position--actual value of the piston 16'the main control valve 11' corresponding middle position 0 of the servocontrol valve 14' which the central longitudinal axis 193 of theabutment shaft 189 and the central longitudinal axis 68' of the servocontrol valve 14' corresponding radial plan of the angle .O slashed.cuts in half, since the radial end face surfaces 191 and 192 of the coilspring 183 carrying end section 186 of the sleeve-shaped housing element99' engage lockingly with each other. This angle .O slashed. is selectedto be sufficiently large, that the central piston 66', which respect tothe represented middle position of the abutment shaft or rod 199 aboutthe maximal deflection angle φ_(1max) and φ_(2max) in clockwise and incounterclockwise sense with respect to the sleeve-shaped housing element99' is rotatable, without that this free-of-play engagement with thepiston 16' of the main control valve 11' is lost.

The one end 194 of the coil spring 183 is secured on the free endsection 189' of the abutment shaft 189, while the other end 196 in closeproximity to the radial face 192, on which sleeve-shaped housing element99' is secured, of which azimuthal spacing from the abutment rod 189,seen from the path direction of the spring 183 corresponds approximatelyto the azimuthal alignment or orientation.

What is claim is:
 1. Electrohydraulic control valve arrangement forcontrolling the pressure media supply to and discharge from a hydraulicmotor, including:a main control valve constructed as a 3-position-valve,which main control valve includes a piston which is displaceable inalternative directions between end positions in a bore of a housing,which end positions correspond to the maximal values of derestrictedcross-section of flow-through paths of the main control valve inalternative functional positions I and II, which steadily increaseessentially with increasing displacement of the piston out of afunctionally neutral center position 0, and is correspondingly reducedwith a nearing of the piston to its center position, and anelectrohydraulic servo control valve which is guided by an electronicsetpoint value, and which controls said main control valve pistondisplacement by the alternating application and relieving of pressure intwo control chambers of the main control valve, whereina) as theelectrohydraulic servo control arrangement an electrohydraulic follow-upservo control valve (14; 14') is provided, which operates withelectromechanically controllable position setpoint input and mechanicalactual position data feedback in order to pilot the main control valvein a manner guided by the setpoint value, and is constructed as a 4/3way valve which has a P-supply connection (76), which is incommunication with the pressure outlet of a pressure supply unit, aswell as a T-return connection (77), which is connected with anunpressurized reservoir of the pressure supply unit, and which furtherhas an A-control connection (78), which is in communication with one ofsaid control chambers (13) of the main control valve (11), and furtherhas as a B-control connection (79), which is in communication with theother of said control chambers (13) of the main control valve (11),wherein in one of the central positions of the main control valve (11)associated central positions of the piston element (66; 66') of thefollow-up servo control valve (14; 14') the supply and the userconnections are closed off against each other, and in the alternativefunctional positions I and II in which the follow-up servo control valve(14; 14') is positioned as a function of the given setpoint value, onthe one hand the A-control connection (78) is in communication with theP-supply connection (76) and the B-control connection (79) is incommunication with the T-return flow connection (77), and on the otherhand the A-control connection (78) of the follow-up servo control valve(14; 14') is in communication with its return flow connection (77) andthe B-control connection (79) is in communication with the P-supplyconnection (76) of the follow-up servo control valve (14; 14'); b) theservo control valve (14; 14') comprises a sleeve-shaped housing element(99; 99') which is disposed to be moveable in a pressure tight manner ina connection block (114, 114') rigidly connected to the housing of themain control valve (11, 11'), and a piston element (66; 66') which isdisposed so as to be moveable in a pressure tight manner in thesleeve-shaped housing element (99; 99'), of which one of these serves asthe setpoint value input element, which by means of a controllableelectro-motor (131) is driveable in alternative directions for carryingout incremental displacements with respect to the other, which serves asactual position feedback element, which is force-form locking movablyconnected with the piston (16, 16') of the main control valve (11, 11')and thereby is controllable for carrying out servo-control movementssynonymous with the displacement of the setpoint value input element,and c) the servo control valve (14; 14') is provided with a valve springarrangement (118, 119; 151), which in a non-controlled state of thesetpoint input motor (131) adjusts the setpoint input element upon thesetpoint input position associated with the operationally neutralcentral position of the main control valve (11; 11').
 2. Control valvearrangement according to claim 1, wherein the main control valve (11)and the servo control valve (14) are constructed as linear slide valves,arranged with their central longitudinal axis (18, 68) running parallel,wherein a return signal element (99) of the servo control valve (14) isconnected or coupled axially fixed against sliding with the piston (16)of the main control valve (11) and the setpoint input element (66) ofthe servo control valve (14) is displaceable axially back and forth bymeans of an electrical linear drive.
 3. Control valve arrangementaccording to claim 1, wherein the main control valve (11') isconstructed as linear slide valve and the servo control valve (14') asrotating slide valve, wherein the actual position feedback element (99')is moveably coupled with the main control valve piston (16') via acoupling arrangement (143, 144), which convert the linear displacementsof the piston (16') of the main control valve (11') into azimuthaldisplacements of the actual position feedback element of the servocontrol valve (14'), and of which the setpoint value input element (66')is connected fixed against rotation with the drive shaft (146) of theelectric setpoint input motor (131).
 4. Control valve arrangementaccording to claim 3, wherein the servo control valve (14') with respectto the central longitudinal axis (18) of the main control valve (11') isso mounted to runs at a right angle with its central longitudinal axis(68) to that of the main control valve (11'), that as actual positionfeedback element the sleeve-shaped housing element (99') of the servocontrol valve (14') is utilized, with which a coupling element (143) isconnected fixed against rotation, which via form fitting engagement witha take-along element (144) of the main control valve piston (16')converts the axial displacement thereof into azimuthal servo movement ofthe feedback element (99').
 5. Control valve arrangement according toclaim 4, wherein the take-along element of the main control valve piston(16') is formed as a ring notch (144) of the same, that the couplingelement (143) extends thereinto with a right angular to the central axis(18) of the piston (16') and parallel to the central longitudinal axis(68) of the servo control valve (14') extending, tab-shaped end segmentof the take along element (144), and that the arrangement of the notch(144) on the piston (16') of the main control valve (11') and that ofthe coupling element (143) on the return signal element (99') of theservo control valve (14') thereupon are determined based upon eachother, so that in the functional neutral center position of the maincontrol valve (14') the longitudinal axis of the tab like couplingelement-segment (143) and the central longitudinal axis (68') of theservo control valve (14') defined planes run right angularly to thecentral longitudinal axis (18) of the main control valve (11'). 6.Control valve arrangement according to claim 5, wherein said engagementend of the coupling element (143) which engages between the notch sidewalls of the ring notch (144) is constructed as a ball head (177), ofwhich the cross-section is greater than that of the tab shaped endsegment, and is approximately the same or at most identical to thethinness separation of the notch wall of the ring notch (144) of themain control valve piston (16') measured in axial direction.
 7. Controlvalve arrangement according to claim 5, wherein a tensioning device(181) is provided, which produces a permanent effective torque betweenthe sleeve-shaped housing element (99') and the piston (66') of theservo control valve (14'), which urges the coupling element (143) inforce locking engagement with the one notch wall of the ring notch (144)of the piston (16') of the main control valve (11') and of which thevalue is smaller than the arrest moment of the setpoint input-motor(131) and is also smaller than the return urging moment exercised in theengaged pressure supply through the piston (16') upon the piston sidehousing element (99') of the servo control valve (14').
 8. Control valvearrangement according to claim 7, wherein the total value .O slashed. ofthe azimuthal deflection of the piston (66') of the servo control valve(14') with respect to the sleeve-shaped housing element (99') is lessthan 180°, thereby characterized, that the azimuthal displacement area.O slashed. through impact effect of an with the piston (66') fixedconnected radial rod or shaft with the aximuthal bordering or limitingof an itself in circumference direction extending long hole of thesleeve-shaped housing element (99') or a face side associated, edgeopen, sector shaped recess of the same is bordered, and that thetensioning device includes an under pull tension standing tensioningspring secured on the one hand in the free end of the shaft and on theother hand in the sleeve-shaped housing element (99'), which is receivedby an open ridge of the sleeve-shaped housing element (99') having acircumference area complimentary to the displacement range or area .Oslashed..
 9. Control valve arrangement according to claim 3, wherein inthe not-driven condition the setpoint input motor (131) the setpointvalue input element (66, 66') therein with the center position of themain control valve piston (16, 16') associated setpoint value inputposition urging spring arrangement is an azimuthally pretensionedhelical coil spring, of which the coil axis coaxially circumscribe thecentral axis (68) of the servo control valve (14, 14'), as a shankspring (151), which has two radial or approximately radial engaging freeshank ends, between which a fixedly with the connection block (114') ofthe servo control valve (14') are connected abutment tab and a fixedagainst rotation with the setpoint value input element abutment tab(156).
 10. Control valve arrangement according to claim 9, wherein atleast one of the windings (158) of the shank spring (151) whichcoaxially circumscribes the central axis of the servo control valve(14') is provided with a bulge, which form fittingly engages an abutmentplug fixedly connected with the connection block (114') of the servocontrol valve (14) and extending parallel to the central longitudinalaxis (68) thereof.
 11. Control valve arrangement according to claim 1,wherein in the not-driven condition of the setpoint input motor (131)the setpoint input element (66; 66') therein with the center position(0) of the main control valve piston (16; 16') associated setpoint inputposition urging valve spring arrangement includes two pretensioned presssprings (118, 119), which biases in opposite directions the setpointvalue input element of the servo control valve.
 12. Control valvearrangement according to claim 11, wherein the pretensioning of thepress springs (118, 119) is adjustable.
 13. Control valve arrangementaccording to claim 11, wherein the tensioning stroke of the valvesprings (118, 119) is limitable by restraining the springs to thatdesired value, in which the central position (0) of the main controlvalve piston (16; 16') the associated position of the setpoint valueelement is achieved.
 14. Control valve arrangement as in claim 1,wherein said controllable electro-motor (131) is a step motor.